Stroke is the most serious complication of longstanding atrial fibrillation (AF; Circulation 123(4): e18-e209 (Feb. 1, 2011); Arch Intern Med 154: 1449-1457 (1994)). Factors that are considered when determining a risk level of stroke for a patient include the patient's history of prior stroke or transient ischemic attack (TIA), presence of hypertension or diabetes, age greater than 75 years, and poor left ventricular function (Arch Intern Med 154: 1449-1457 (1994)). The identification of these factors led to the development of several risk stratification schemes (Gage, et al., JAMA 285(22): 2864-2870 (2001); Wang, et al., JAMA 290(8): 1049-1056 (2003)), including the CHADS2 risk scheme (Gage, et al., 2001, supra), where C stands for congestive heart failure, H for hypertension, A for age greater than or equal to 75 years, D for diabetes and S for prior strokes or TIAs. In the CHADS2 risk scheme, one point is assigned for the patient having a medical history of each of congestive heart failure, hypertension, age greater than or equal to 75 years, and diabetes, while two points are assigned when a patient has a history of TIA or stroke. It is believed that the frequency of stroke (adjusted stroke rate per 100 patient-years) increases as a CHADS2 score increases (Gage, et al., 2001, supra).
The CHA2DS2-VASc score represents another risk scheme used to determine risk level of stroke. In the CHA2DS2-VASc scheme, the same factors considered in the CHADS2 score are considered, but the CHA2DS2-VASc scheme additionally considers non-major stroke risk factors, including patient age between 65 and 74 years, female gender, and vascular disease.
While such risk stratification schemes have been found to be helpful in determining a patient's risk level for stroke and thus a patient's need for stroke prevention medication, e.g., anti-coagulation therapy, when the patient exhibits chronic AF, there nevertheless remains a need for a more accurate risk prediction model, especially in patients who fall in the intermediate risk category on these risk scores.